As known, a “manual” treadmill is a motorless exercise machine which is manually actuated by the user by means of the interaction of the lower limbs with the walking/running belt.
A manual treadmill typically comprises a frame extending along a longitudinal direction of development parallel to the advancing direction of the user while walking or running.
Furthermore, such a manual treadmill comprises a first front rotation shaft and a second rear rotation shaft about which a walking/running belt is wound.
The walking/running belt of the user is typically mounted on the first front rotation shaft and on the second rear rotation shaft so as to have a curved side profile along, and respect to, the longitudinal direction of development of the frame on the part facing upwards, i.e. having a first descending portion starting from the first front rotation shaft and a second portion, opposite to the first portion, ascending towards the second rear rotation shaft.
While the user runs or walks on the walking/running belt, the weight force exerted by the user at the first descending portion of the walking/running belt allows to transform the potential energy into kinetic energy and to generate, accordingly, the rotation of the walking/running belt from the first front rotation shaft to the second rear rotation shaft by means of the interaction of the user's lower limbs with the walking/running belt alone.
The curved manual treadmill described above has the disadvantage of allowing the user to simply walk or run or, in all cases, perform a very limited number of physical exercises.
Nowadays, instead, the need is strongly felt to have exercise machines, and thus curved manual treadmills, which are as versatile as possible so as to allow a user to perform the largest possible number of mutually different, cardiovascular and muscle strength and strengthening physical exercises, even with a single exercise machine, and thus at low cost.